Electron discharge tube with metal foil electrode



` May 17,1949. l I J. 1 H. JoNKER ETAL .2,470,248 v ELECTRON DISCHARGETUBE WITH. METAL FOIL ELECTRODE Filed Aug. 17, 1946 CPEEN GRID //VPatented May 17, 1949 Niven TENT FFICE ELECTRON DISCHARGE TUBE WITHMETAL FOIL ELECTRODE Application August 17, 1946, Serial No. 691,334 InBelgium May 1, 1945 Section 1, Public Law 690, August 8, 1946 Patentexpires May 1, 1965 4 Claims.

This invention relates to an electric discharge tube having an electrodesystem which comprises at least a cathode, an anode and one or moreintermediate auxiliary electrodes.

These auxiliary electrodes, for instance, controland screen-electrodes,are usually shaped as a wire-grid consisting of a certain number of thinwires spaced apart from each other, thus leaving apertures for thepassage of electrons. In this case the grid must be designed in such amanner as to be capable of acting suiciently upon the electron stream byvoltage variations. Furthermore, notably in the case of screen grids,the ratio between the surface area of the apertures and that of thewires must be such that not too many electrons are intercepted and flowoif as screen-grid current, such a grid nevertheless having to functionas an electrostatic screen between the electrodes located at both sidesthereof. In many cases a compromise has to be arrived at in determiningthe size of the apertures of the grid and the thickness of the wires. Ofcourse, one is bound to the mechanical possibilities of working up suchgrids.

Very satisfactory results are obtained by making use of an electricdischarge tube according to the invention, the electrode system of whichconsists of a cathode, an anode and one or more intermediate auxiliaryelectrodes, one auxiliary electrode consisting at least partly of a thinmetal lm.

When making use of this construction a complete electrostatic shieldingis obtained and the permeability to electrons is quite satisfactory.Therefore this construction is particularly suitable for use in the caseof screen grids, though it is also feasible, for instance intransmitting tubes, to design control-electrodes in this way. For actingupon the electron stream these electrodes, which consist of a metalfilm, yield a very uniform field, since there are no apertures throughwhich extends the field of a neighbouring electrode.

The lm must be very thin and be made from suitable material. As such wemay mention metals, for instance gold, nickel, copper and silver, thelast-mentioned metal more particularly giving excellent results. Thethickness of the lm should not exceed 0.2;. Fr instance, it has been(Cl. Z50-27.5)

2 found that when making use of a silver film having a thickness ofabout 0.1 the permeability to electrons amounts to 30 to 50% whenapplying a voltage of +3 to the nlm. More particularly at these lowvoltages the electron permeability is high.

These lms can be made in a manner known. According to a very suitablemethod, a film is secured to a frame, for instance grid-shaped, toconstitute the support, from a chemical bath on which a very thin layerof silver deposits, which constitutes the film proper, by immersion ofthe frame, after which it is lifted under the film so thatthe latterrests on the frame. 1f desired, this may take place by siphonage of theliquid.

According to another known method, a nickellm is precipitatedelectrolytically or by vaporisation on a polished steelplate, whereafterthe steelplate is solved chemically. Instead of a steelplate, one canuse a Celluloid plate. Then the metal lm is applied to a frame andeventually glued.

What we `claim is:

1. An electron discharge tube comprising a cathode, an anode and anauxiliary electrode interposed between said cathode and anode, saidauxiliary electrode comprising a metal foil having a thickness of theorder about 0.1@ to 0.2# and having at potentials thereof of the orderof 3 volts positive relative to said cathode an electron permeability ofthe order of 30% to 50%.

2. An electron discharge tube comprising a cathode, an anode, a controlgrid interposed between the cathode and anode, and a screen gridinterposed between said control grid and said anode, said screen gridcomprising a metal foil having a thickness of the order of 0.1M to 0.2,aand having at potentials thereof of the order of 3 volts positiverelative to said cathode an electron per.- meability of the order of 30%to 50%.

3. An electron discharge tube comprising a cathode, an anode and anauxiliary electrode interposed between said cathode and anode, saidauxiliary electrode comprising a silver foil having a thickness of theorder of about 0.1@ `and having at potentials thereof of the order of 3volts positive relative to the cathode an electron permeability of theorder of 30% to 50%.

4. An electron discharge tube comprising a cathode, an anode, a controlgrid interposed between the cathode and anode, and a, screen gridREFERENCES CITED interposed between the control grid and the anode, saidscreen grid comprising a foil of a metal selected from the groupconsisting of gold, copper The following references are of record in thefile of this patent:

and silver, said foil having a thickness of the or- 5 UNITED STATESPATENTS der of about 0.111. to 0.211 and having at potentials NumberName Date thereof of the order of 3 volts positive relative to 1,543,033snemng June 23, 1925 said cathode aneleotronpermeablhty of the Order1,934,477 Barton Nov. '7, 1933 1 of 30% tof5o%. i m FOREIGN PATENTSJOHAN LODEWIJK HENDRIK J ONKER. Number Country Date GESINUS DIEMER.350,938 Great Britain June 15, 1931

